The present invention is directed to novel analogues of PACAP (Pituitary Adenylate Cyclase Activating Polypeptide) and the use thereof for treating the conditions and or diseases as described herein.
A review of PACAP and its physiological function is summarized in Christophe, J., Biochimica et Biophysica Acta, 1154, 183-199 (1993), as follows.
PACAP a member of a super family that already includes several regulatory peptides, e.g., VIP, PHI, PHV, secretin, helodermin, helospectin I and II, glucagon, GIP and GRF. This biologically active neuropeptide exists in two amidated forms: PACAP(1-38)-NH.sub.2 (PACAP-38) and PACAP(1-27)-NH.sub.2 (PACAP-27). The deduced amino acid sequence of PACAP-38 in man (Kimura, C., et al., Biochem. Biophys. Res. Commun., 166, 81-89, (1990)) and rat (Ogi, K., et al., Biochem. Biophys. Res. Commun., 173, 1271-1279, (1990)) is identical to that of the isolated ovine PACAP-38.
At least two classes of PACAP receptors have been described in mammalian tissues and cell lines: type I PACAP-preferring receptors and type II receptors which bind PACAP-27, PACAP-38 and VIP (vasoactive intestinal peptide) (Cauvin, A., et al., Peptides, 11, 773-777 (1990) and Shivers, B. D., et al., Endocrinology, 128, 3055-3065 (1991)). In addition, the first type is capable to display two subtypes, and the second type can be tentatively divided into three subtypes.
Type I is highly selective in that it recognizes PACAP-27 and PACAP-38 much more potently than VIP. PACAP-38 and PACAP-27 can thereafter activate adenylate cyclase with the same high potency and efficacy. Type I receptors may, however, be present as two coexisting subtypes (or states) based on radioligand binding. In rat brain membranes (Cauvin, A., et al., Regul. Pept. 35, 161-173, (1991)), the PACAP-A subtype exhibits hardly any preference for PACAP-38 over PACAP-27, whereas the PACAP-B subtype recognizes PACAP-38 with high affinity and PACAP-27 with low affinity.
The type II receptor is the classical VIP receptor. Based on binding affinity and adenylate cyclase activation, it now appears that the type II receptor is non-selective since it shows similar high affinity for PACAP-27, PACAP-38 and VIP.
A relatively comprehensive spectrum of pharmacological activities has already been established for the physiological roles of PACAP.
Concerning the hypothalamo-pituitary axis, PACAP reduces food intake in mice and raises plasma arginine vasopressin in rat, probably through PACAP-ir (ir=immunoreactive) neurons in paraventricular and supraoptic nuclei projecting to the neurohypophysis. PACAP originating in the hypothalamus may also be transported to the anterior pituitary through portal vessels. Data on the antehypophysis suggest a role on i.a. reproduction and growth. PACAP stimulates adenylate cyclase and increases [Ca.sup.2+ ] in gonadotropes, somatotropes, and folliculostellate cells. It elevates the secretion of .alpha.-MSH from melanotropes, and that of interleukin-6 from pituitary folliculo-stellate cells. PACAP potentiates the effects of LHRH (or GnRH, gonadotropin releasing hormone) on LH (lutenizing hormone) and FSH secretion. More clearly perhaps, PACAP increases the synthesis of LH, GH (growth hormone), PRL (prolactin) and ACTH after 1-2 days. In human pathology, PACAP-27 and PACAP-38 stimulate adenylate cyclase activity in membranes from "null", gonadotropin-, GH-, and ACTH-producing pituitary adenomas.
In brain, and outside the hypothalamus, PACAP stimulates the synthesis of melatonin from pinealocytes and may play a role in the integration of visual inputs and in memory. The widespread distribution of specific type I PACAP receptors contrasts with the more focused localization of type II VIP-PACAP receptors. Type I receptors in the rabbit eye may contribute to the physiology of the retina and choroid. In general, the neuronal increases in cAMP and Ca.sup.2+ could contribute to early brain development, repair, and modification of circuitry, with the help of neurotropic factors from astrocytes that are also stimulated by PACAP.
Type I receptors represent a minority (20%) as compared to type II receptors in rat liver. PACAP directly relaxes the digestive tract motility via activation of apamin-sensitive calcium-activated K.sup.+ channels and is an anion secretory neuropeptide on rat jejunal mucosa, possibly through submucous neurons. PACAP contracts the gallbladder in conscious dog by a preganglionic mechanism. In vivo it increases amylase secretion via a cholinergic mechanism in dog and glucagon release in mice.
PACAP provokes the hypersecretion and synthesis of catecholamines from the rat adrenal and facilitates mitosis, neurite genesis, and survival of cultured rat sympathetic neuroblasts. A bolus i.v. injection of PACAP induces a biphasic change in blood pressure (decrease followed by increase) that is accompanied by a biphasic change in systemic vascular resistance. The pressor response is due to the release of catecholamines from the adrenal gland. The relaxant action of PACAP in isolated rabbit precontracted aortic rings is 100-fold more potent than VIP, surprisingly durable, and endothelium-independent. PACAP is also a potent microvasodilator in human skin and here its action is long lasting again. PACAP-38 causes an increase in beating rate in neonatal rat cardiomyocytes and stimulates adenylate cyclase in purified sarcolemmal membranes from porcine and canine ventricles. PACAP relaxes the airway and vascular smooth muscle in guinea-pig, rat and cat lung. PACAP-ir is abundant in the rat testis and type I receptors in spermatozoa may play a role in sperm motility.
In addition, PACAP may intervene in ontogenetic processes in the nervous system and modulate mitogenesis and differentiation (e.g., neurite outgrowth) in several cell lines where maligancy is sometimes at the origin of type I receptor emergence.
Therefore, there is a keen interest to find analogues of PACAP which are more active than PACAP-27 and/or PACAP-38 and/or which possess a longer half-life in a patient.
U.S. Pat. No. 5,208,320 discloses certain peptides that produce c-AMP activity. Robberecht, P., et al., Molecular Pharmacology 42:347-355, (1992) discloses a series of PACAP-27 and PACAP-38 analogues. PCT publication no. WO 96/09064 discloses a series of PACAP analogues for use in preventing or treating brain damage.